Field of the Invention
The invention relates to a method for cooling a plant for superconductive cables which includes two thermally insulated end closures and at least one thermally insulated, tubular cryostat, in which at least one superconductive cable is arranged by means of which liquid nitrogen contained in a cooling agent supply is pumped by means of a pump through a first end closure and the cryostat to a second end closure (EP 2 328 156 A1).
Description of Related Art
In today's technology, superconductive cables have electrical conductors of a composite material containing ceramic material that changes over into the superconductive state at sufficiently low temperatures. The electrical direct current resistance of a correspondingly built conductor is zero with sufficient cooling, as long as a certain voltage has not been exceeded. Suitable ceramic materials are, for example, BSCCO (bismuth-strontium-calcium-copper oxide) as material of the first generation or ReBCO (rare-earth-barium, copper oxide), particularly YBCO (yttrium-barium-copper oxide) as materials of the second generation. In conventional technology, such superconductive conductors are cooled with liquid nitrogen which, for this purpose, has a temperature of operation of usually less than 77K.
For cooling the nitrogen to the stated temperature, known methods utilize cooling units to which pumps are connected by means of which liquid nitrogen is pumped with sufficient pressure into an end closure and through the cryostat to the other, second end closure. Such a method is described, for example, in the above mentioned EP 2 328 156 A1. The nitrogen can be conveyed from the second end closure for renewed cooling to operating temperature by a suitable pipe to the respective cooling unit. This unit is, in its totality, complicated and the known cooling units have parts which are subject to wear and may have to be replaced if necessary. Therefore, such a cooling unit requires continuous maintenance.